Message 410684 - Python tracker

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Author	mark.dickinson
Recipients	Dennis Sweeney, mark.dickinson, serhiy.storchaka, steven.daprano, terry.reedy
Date	2022-01-16.08:50:07
SpamBayes Score	-1.0
Marked as misclassified	Yes
Message-id	<1642323008.02.0.562629754476.issue46393@roundup.psfhosted.org>
In-reply-to

Content
[Terry] > To avoid the intermediate set, [...] It's not quite as bad as that: there _is_ no intermediate set (or if you prefer, the intermediate set is the same object as the final set), since the frozenset call returns its argument unchanged if it's already of exact type frozenset: >>> x = frozenset({1, 2, 3}) >>> y = frozenset(x) >>> y is x True Relevant source: https://github.com/python/cpython/blob/09087b8519316608b85131ee7455b664c00c38d2/Objects/setobject.c#L999-L1003

[Terry]
> To avoid the intermediate set, [...]

It's not quite as bad as that: there _is_ no intermediate set (or if you prefer, the intermediate set is the same object as the final set), since the frozenset call returns its argument unchanged if it's already of exact type frozenset:

>>> x = frozenset({1, 2, 3})
>>> y = frozenset(x)
>>> y is x
True

Relevant source: https://github.com/python/cpython/blob/09087b8519316608b85131ee7455b664c00c38d2/Objects/setobject.c#L999-L1003

History
Date	User	Action	Args
2022-01-16 08:50:08	mark.dickinson	set	recipients: + mark.dickinson, terry.reedy, steven.daprano, serhiy.storchaka, Dennis Sweeney
2022-01-16 08:50:08	mark.dickinson	set	messageid: <1642323008.02.0.562629754476.issue46393@roundup.psfhosted.org>
2022-01-16 08:50:08	mark.dickinson	link	issue46393 messages
2022-01-16 08:50:07	mark.dickinson	create